Polishing pad with a partial adhesive coating

ABSTRACT

A method for selectively altering a polishing pad adhesive layer includes providing a mask having transparent regions and opaque regions and directing radiation toward the mask so that the radiation passes through the transparent regions and impinges onto the adhesive layer on the polishing pad. The area of the adhesive layer corresponding to the transparent regions of the mask is cured to be less adhesive. The area of the adhesive layer corresponding to the opaque regions remain adhesive.

BACKGROUND

[0001] The invention relates to chemical mechanical polishing ofsubstrates, and more particularly to a polishing pad with a partialadhesive coating, and to methods and apparatus for producing suchpolishing pads.

[0002] Integrated circuits are typically formed on substrates,particularly silicon wafers, by the sequential deposition of conductive,semiconductive or insulative layers. After each layer is deposited, thelayer is etched to create circuitry features. As a series of layers aresequentially deposited and etched, the outer or uppermost surface of thesubstrate, i.e., the exposed surface of the substrate, becomessuccessively more non-planar. If the outer surface is non-planar, thenphotolithographic techniques to pattern photoresist layers might not besuitable, as a non-planar surface can prevent proper focusing of thephotolithography apparatus. Therefore, there is a need to periodicallyplanarize this substrate surface to provide a planar layer surface.

[0003] Chemical mechanical polishing is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier or polishing head, with the surface ofthe substrate to be polished exposed. The substrate is then placedagainst a rotating polishing pad. In addition, the carrier head mayrotate to provide additional motion between the substrate and polishingsurface. Further, a polishing slurry, including an abrasive and at leastone chemically-reactive agent, may be spread on the polishing pad toprovide an abrasive chemical solution at the interface between the padand substrate.

[0004] A typical polishing pad includes a hard top layer and a softerbottom layer. The top layer has a high friction polishing surface,capable of transporting slurry, and a second surface adhesively bondedto a first surface of the bottom layer. A second surface of the bottomlayer is typically attached to a platen by a high strengthpressure-sensitive adhesive layer.

[0005] One consideration in the production of integrated circuits isprocess and product stability. To achieve a low defect rate, eachsubstrate should be polished under similar conditions, i.e., samepolishing surface structure. A limitation on process stability, as wellas polishing throughput, is “glazing” of the polishing pad. “Glazing”occurs when the polishing pad is frictionally heated and compressed inregions where the substrate is pressed against it, as well as worn as aresult of the abrasive contact. The peaks of the polishing pad arepressed and worn down and the pits of the polishing pad are filled up,so the surface of the polishing pad becomes smoother and less abrasive.As a result, the polishing time required to polish a substrateincreases. Therefore, the polishing pad surface must be periodicallyreturned to a more uniform abrasive condition, with higher friction andability to transport slurry. This process is defined as “conditioning”and serves the purpose of maintaining a high polishing rate. Theconditioning process can be destructive for the polishing pad andresults in reducing the lifetime of the polishing pad. Because of thesereasons the polishing pad needs to be removed from the platen andreplaced every 100 to 1000 substrates, depending upon the type ofsubstrate and conditioning process.

[0006] In order to remove the pad, an operator reaches into thepolishing area, grasps the polishing pad by hand or with mechanical aidsand pulls it to peel it off the platen. Because of the high strength ofthe adhesive layer, the operator must apply a large force to pull thepolishing pad off the platen. For example, the operator may need toapply pulling force of approximately 100 pounds. This large force canexceed the physical abilities of the operator and can pose a risk ofinjury.

SUMMARY

[0007] In general, in one aspect, the invention features a polishing padincluding a first layer having a polishing surface, and a second layerhaving an adhesive region and a cured region disposed on a surface ofthe first layer opposite the polishing surface.

[0008] Implementations of the invention may include one or more of thefollowing features. The polishing pad may have a plurality of adhesiveand cured regions. The cured regions may be partially or entirely cured.The cured regions may be circles or arc segments arranged in a pattern.The cured region and the adhesive region may form concentric circles. Athird layer may be disposed between the first and second layers oppositethe polishing surface.

[0009] In general, in another aspect, the invention features anapparatus for selectively altering a polishing pad adhesive layer. Theapparatus includes a radiation source generating a radiation beam, asupport for the polishing pad, and a mask having a transparent regionand an opaque region. The mask is disposed between the radiation sourceand the substrate holder, such that the radiation passes through thetransparent region and is blocked by the opaque region. A shutter may bedisposed between the radiation source and the mask.

[0010] In general, in another aspect, the present invention features amethod for selectively altering a polishing pad adhesive layer. Themethod includes: providing a mask having a transparent region and anopaque region and directing radiation toward the mask so that theradiation is blocked by the opaque region and passes through thetransparent region to impinge on the adhesive layer on the polishingpad, whereby the area of the adhesive layer corresponding to thetransparent region of the mask is cured to be less adhesive.

[0011] Implementations of the invention may include one or more of thefollowing features. The radiation may be ultraviolet light. Thetransparent region may be made of ultraviolet light transparent quartzor polymer material. The mask may be made of ultraviolet light blockingmaterial such as paper metal, ceramic or polymer material. Thetransparent region may be an opening in the mask. The transparent regionand the opaque region may form concentric circles. The mask may have aplurality of transparent and opaque regions. The transparent regions maybe circles or arc segments arranged in a pattern. The ratio of the curedregion surface to the adhesive region surface may be between about 10 to30%. The polishing pad may be exposed to the radiation for a timevarying between about 5 to 60 seconds. The radiation intensity may varybetween about 100 to 1200 Watts/inch.

[0012] In general, in another aspect, the invention features a methodfor selectively altering a polishing pad adhesive layer. The methodincludes: providing a polishing pad having a layer of adhesive thatcovers substantially an entire surface of the pad, and curing selectedportions of the adhesive layer to reduce adhesive strength of the layer.

[0013] Among the advantages of the invention may be one or more of thefollowing. By selectively altering a polishing pad adhesive layer thestrength of the adhesive layer is reduced. This reduces the forceapplied to remove the polishing pad off the platen and the risk ofinjury for an operator.

[0014] Other features and advantages of the invention will be apparentfrom the following description of the preferred embodiments, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a chemical mechanical polishingapparatus.

[0016]FIG. 2 is a diagrammatic cross-sectional view of a polishing pad.

[0017]FIG. 3 is a flow diagram describing the method for fabricating apolishing pad with adhesive and non-adhesive regions.

[0018]FIG. 4 is a diagrammatic cross-sectional view of a polishing padbeing exposed to ultraviolet (UV) radiation through a mask.

[0019]FIG. 4A is a diagrammatic cross-sectional view of a polishing padhaving a paper mask disposed on the adhesive layer.

[0020]FIG. 5 is a top view of a UV mask having a “polka dot” pattern.

[0021]FIG. 6 is a top view of a UV mask having a ring pattern.

[0022]FIG. 7 is a top view of a UV mask having a ring and arc segmentpattern.

[0023]FIG. 8 is a diagrammatic view of an apparatus for selectivelyremoving an adhesive layer from a polishing pad.

DETAILED DESCRIPTION

[0024] Referring to FIG. 1, a polishing apparatus 10 includes a housing12 that contains three independently-operated polishing stations 14, asubstrate transfer station 16, and a rotatable carousel 18 whichchoreographs the operation of four independently rotatable carrier heads20. A more complete description of the polishing apparatus 10 may befound in U.S. Pat. No. 5,738,574, the entire disclosure of which isincorporated herein by reference.

[0025] Each polishing station 14 includes a rotatable platen 110 whichsupports a polishing pad 100. The platen 110 is mounted to a table top57 inside the polishing apparatus 10. In operation, a substrate 30 isloaded to the transfer station 16, from which the substrate istransferred to a carrier head 20. The carousel 18 then transfers thesubstrate through a series of one or more polishing stations 14 andfinally returns the polished substrate to the transfer station 16. Eachcarrier head 20 receives and holds a substrate, and polishes it bypressing it against the polishing pad 100 on platen 110.

[0026] Referring to FIG. 2, one type of a polishing pad 100 includes afifty mil thick hard layer 102, a fifty mil thick softer layer 104, anda pressure sensitive adhesive lower layer 106. The hard layer 102 istypically a material composed of polyurethane mixed with other fillers.The softer layer 104 is typically a material composed of compressed feltfibers leached with urethane, and adhesive layer 106 is a rubber-basedor acrylic based adhesive. The hard layer 102 is adhesively bonded tothe softer layer 104 by a bonding layer 107. The thickness of thepolishing pad may vary between 30 to 250 mils. A polishing pad, with ahard layer composed of IC-1000, a softer layer composed of SUBA-4, and alayer composed of a rubber-based adhesive, is available from Rodel,Inc., located in Newark, Del. (IC-1000 and SUBA-4 are product names ofRodel, Inc.). The adhesive layer 106 covers the entire bottom area ofthe polishing pad and has one surface 111 attached to layer 104 and asecond surface 109 which is to be attached to the platen. The polishingpad is supplied with this second surface 109 covered with a lining 108,to prevent accidental adhesion of the pad. The lining 108 is removedbefore installing the polishing pad on the platen.

[0027] The force applied to remove the polishing pad from the platendepends upon the size of the area covered with the adhesive and the typeof the adhesive. The entire bottom surface of the pad is usually coveredwith a continuous adhesive layer. The strength of the adhesive layer maybe reduced by making selected portions of the adhesive layer lessadherent. Specifically, selected areas of the adhesive layer may bepartially or entirely cured to reduce their adhesive strength. Forexample, the selected areas of the adhesive layer may be exposed toultra-violet (UV) light in the presence of air, as this cures therubber-based adhesive to make it less adherent.

[0028] Referring to FIG. 3, the method 200 of producing a polishing padwith a partial adhesive layer includes providing a polishing pad with alayer of adhesive that covers the entire lower surface of the pad andremoving the protective lining that covers the adhesive layer (step202), positioning a mask with openings of a predetermined size over theadhesive layer (step 204), exposing the adhesive layer to UV light for apredetermined time (step 206), and then removing the mask and applyingthe pad onto the platen (step 208). After completing the polishingprocess the pad may be easily peeled away from the platen due to thereduced strength of the adhesive layer.

[0029] Referring to FIG. 4, the areas 105 of the adhesive layer 106 thatare to be exposed to UV light are selected by using a mask 120. The mask120 includes windows 124 which are transparent to UV light, and opaqueareas 122 which block UV light. The mask material may be paper, metal,polymer or ceramic material, or regular borosilicate glass that blocksUV light. The transparent windows may be openings formed in the mask, UVtransparent suprasil type quartz, or certain types of polymer materialswhich are UV-transparent. The areas 105 of the adhesive layer 106 thatare exposed to the UV light are cured and the areas 103 that do notreceive the UV light remain adhesive. In one example, the mask 120 maybe a paper having openings 124 and being attached to the adhesive layer106 (FIG. 4A). The paper mask may be covered with a lining 108.

[0030] Referring to FIG. 5, mask 120 is circular and has a diameterequal to or greater than the diameter of the polishing pad. Differentpatterns for the UV windows and complementing UV blocking areas areshown in FIGS. 5, 6 and 7. They include transparent “polka dot” windows124 (FIG. 5) having a diameter between ¼ to ½ inch, a UV blocking ring122 (FIG. 6) or a narrow outer ring connected to an inner circle by arcsegments 122 which alternate with UV windows 124 (FIG. 7). The patternof transparent and opaque mask areas is replicated in the cured andadhesive areas of the polishing pad, respectively.

[0031] The ratio of the surface area of the cured areas 105 to thesurface of the adhesive areas 103 determines the strength of theadhesive bond between the polishing pad and the platen. The ratio of thesurface of the cured areas to the adhesive areas may vary between about10% to 30%. Several cured areas, each cured area occupying a smallsurface, are used to prevent formation of wrinkles on the polishing pad.

[0032] The cured areas may be located near the center of the polishingpad to avoid large shear stresses and delamination of the polishing padfrom the platen during polishing.

[0033] The degree of curing depends upon the exposure time and theintensity of the UV light source. Short exposure times and low UV lightintensities cause partial curing, whereas long exposure times and highUV light intensities cause complete curing of the adhesive. Exposuretimes may vary between 5 to 60 seconds, and UV power levels may varybetween 100 to 600 Watts/inch. In one example a UV light of 100Watts/inch is used and the exposure time may vary between 5 to 30seconds for a rubber based adhesive.

[0034] Referring to FIG. 8, an apparatus 150 for selectively curing anadhesive layer includes a UV source 140, a mask 120 supported by a maskholder 128, a shutter 130 for blocking the UV-light to the polishing pad100 and a support or holder 132 supporting the polishing pad. The UVsource has a fast linear ramp-up and ramp-down mechanism, and variableintensity high enough to fully cover the polishing pad surface and lowenough to avoid build up of heat in the pad. In one example, the UVsource 140 is a UV lamp from UV Systems, Gaithersburg, Md. having anintensity that can be linearly ramped-up to 600 Watts/inch. In otherexamples, a UV source having a 20 inch long bulb and being rated at 1200Watts/inch is used to irradiate a circular polishing pad along itsdiameter.

[0035] One embodiment of the present invention has been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

[0036] Accordingly, other embodiments are within the scope of thefollowing claims.

What is claimed is: 1.-21. (Cancelled)
 22. A method for selectivelyaltering the adhesive strength of a polishing pad adhesive layer,comprising: providing a mask having a transparent region and an opaqueregion; directing radiation toward the mask so that the radiation isblocked by the opaque region and passes through the transparent regionto impinge on the adhesive layer on the polishing pad, whereby the areaof the adhesive layer corresponding to the transparent region of themask is cured to be less adhesive.
 23. The method of claim 22 whereinthe radiation is ultraviolet light.
 24. The method of claim 23 whereinthe transparent region is made of ultraviolet light transparent quartzor polymer material.
 25. The method of claim 23 wherein the mask is madeof ultraviolet light blocking material.
 26. The method of claim 25wherein the mask is made of metal.
 27. The method of claim 25 whereinthe mask is made of ceramic or polymer material.
 28. The method of claim25 wherein the mask is made of paper.
 29. The method of claim 22 whereinthe transparent region is an opening.
 30. The method of claim 22 whereinthe transparent region and the opaque region form concentric circles.31. The method of claim 22 wherein there are a plurality of transparentand opaque regions.
 32. The method of claim 31 wherein the transparentregions are circles.
 33. The method of claim 31 wherein the transparentregions are arc segments.
 34. The method of claim 22 wherein a ratio ofa surface area of the cured region to a surface area of the adhesiveregion is between about 10% to 30%.
 35. The method of claim 22 whereinthe polishing pad is exposed to the radiation for a time between about 5to 60 seconds.
 36. The method of claim 23 wherein the radiationintensity is between about 100 to 1200 Watts/inch.
 37. A method forselectively altering the adhesive strength of a polishing pad adhesivelayer, comprising: providing a polishing pad having a layer of adhesivethat covers substantially an entire surface of the pad; and curingselected portions of the adhesive layer to reduce adhesive strength ofthe layer.
 38. The method of claim 37 wherein: curing includes directingradiation toward the adhesive layer.
 39. The method of claim 38, furthercomprising: positioning a mask between the adhesive layer and a sourceof radiation, where the mask has a transparent and a non-transparentportion, the non-transparent portion blocks a fraction of the radiationfrom the adhesive layer so that only a selected area of the adhesivelayer is cured.
 40. The method of claim 37, wherein: the adhesive ispartially cured.
 41. The method of claim 37, wherein: the adhesive isfully cured.
 42. The method of claim 37, wherein: the adhesive isacrylic based.
 43. The method of claim 25, wherein: the mask is made ofborosilicate glass.
 44. The method of claim 22, wherein: the transparentregion is in the center of the mask.
 45. The method of claim 22,wherein: the adhesive is rubber based.